In conventional earthworking equipment employing a boom or a boom-like structure, the boom usually must be placed in a special position if the boom is to remain attached to the machine, usually a tractor, when that machine is transported from one work site to another. This position is often referred to as the transport or "transportation position." In such a position the boom is generally brought as close to the center of gravity of the tractor as possible. This is done to improve the stability of the tractor while moving on the open road and to minimize the space occupied by tractor when it is placed in storage. Proper protection of personnel and equipment demands that a positive means be used to hold the boom in the transport position.
In addition, the boom is locked in a near vertical position when it is desired to lift payloads using the earthworking tool attached to the boom. This operation is often referred to as "craning." Locking the boom mechanically when the boom is used like a crane allows the available hydraulic power to be used by the moving components pivoted to the boom.
A representative item of earthworking equipment employing a boom is a backhoe. Backhoes normally consist of a boom that is pivoted on a tractor by a fluid ram and an earthworking tool or bucket assembly that is pivoted on the free end of the boom by a second fluid ram. During transportation or storage, the boom and equipment attached thereto are positioned so as to occupy the least floor space. In addition, this makes movement on public roads more convenient and stable since the center of gravity is shifted closer to the tractor wheels.
A transport position is generally disclosed in Long et al., U.S. Pat. No. 3,376,984. In that patent, the boom is swung to a transport position that is generally vertical and slightly forward of the vertical axis extending through the boom and its support. The boom was held locked in the transport position by the boom fluid ram which had gone "over-center". While that arrangement is acceptable, there are times when it is desirable to positively interlock the boom and its support without relying on the fluid in the boom rams.
One method of positively interlocking the boom and its support without relying on the fluid in the boom rams is disclosed in Shumaker et al., U.S. Pat. No. 3,811,582 and assigned to the assignee of the present invention. Other methods are disclosed in U.S. Pat. Nos. 3,921,835 and 4,184,803. Because of the competitive nature of the industry, manufacturers are constantly striving for improvements which will reduce costs without sacrificing any operational characteristic. A simplified reliable boom lock would be welcomed by the industry.